The present invention relates generally to a pneumatic cushion and manufacturing method therefor. More particularly, the invention relates to a pneumatic cushion made from a thin elastic sheet which can be repeatedly inflated, and a method for manufacturing the pneumatic cushion.
FIG. 1 shows a typical construction of a conventional pneumatic cushion used, for example, for adjusting the firmness of that part of a vehicle seat supporting the lumbar-vertebra area of a passenger's back. As shown in FIG. 1, the pneumatic cushion 10 comprises two pieces of thin elastic sheets 12 and 14 such as a thermoplastic synthetic resin and the like. The sheets 12 and 14 are bonded or welded at a circumferential portion 16 in an air-tight fashion so that a pneumatic chamber 18 is defined therebetween. In the example shown, sheet 14 is provided with an inlet/outlet port 20 for inflating and deflating the cushion.
In such conventional construction, a tension force, as represented by arrows in FIG. 1, is applied to circumferentially extending welded portion 16. If the cushion is subjected to repeated inflation, the internal pressure in pneumatic chamber 18 is repeatedly varied and welded portion 16 is apt to weaken and cause leakage of the air seal. This leakage degrades the usefulness of the pneumatic cushion. Generally, the durability of the welded portion of the cushion is less than the strength of the resin sheet itself. When the pneumatic cushion is used for lumbar support in the vehicle seat, the internal pressure in the pneumatic chamber is frequently varied in response to passenger movement and individual adjustment to achieve the desired firmness. This may possibly cause "weakening or rupturing of the welded portion, resulting in"; leakage of air from the pneumatic chamber.